1. Field of the Invention
The present invention relates to a ZrO2—Al2O3 composite ceramic material with excellent mechanical properties, and a method of producing the same.
2. Disclosure of the Prior Art
As compared with metal and plastic materials, ceramic materials demonstrate excellent hardness, wear resistance, heat resistance and corrosion resistance. As for practical use of the ceramic materials in various application fields, for example, biomaterial parts such as artificial joint and artificial tooth, medical equipments, cutting tools such as drill and surgical knife, mechanical parts for automobile, airplane and space craft used under severe conditions, it is desired to develop a ceramic material having further improved mechanical strength and toughness in a high level. In recent years, a zirconia (ZrO2)-alumina (Al2O3) composite ceramic material has received attention as a potential candidate of the ceramic material.
For example, Japanese patent Early publication [kokai] No. 5-246760 discloses a ZrO2-based composite ceramic sintered body comprising a matrix phase of tetragonal ZrO2 grains containing 5 to 30 mol % of CeO2 and a dispersion phase of fine grains of at least one of selected from the group consisting of Al2O3, SiC, Si3N4 and B4C, which are dispersed within the ZrO2 grains and at grain boundaries of the matrix phase. By the presence of the dispersion phase, a grain growth of the matrix phase is prevented and a fine grained structure of the matrix phase is obtained, so that significant strengthening is achieved mainly due to a reduction in flaw size of the fracture origin.
In addition, U.S. Pat. No. 5,728,636 discloses a ZrO2-based ceramic material having high mechanical strength and toughness, which comprises a tetragonal ZrO2 phase of ZrO2 grains having an average grain size of 5 μm or less, and containing 8 to 12 mol % of CeO2 and 0.05 to 4 mol % of TiO2 as a stabilizer, and an Al2O3 phase of Al2O3 grains having an average grain size of 2 μm or less. In this ceramic material, the Al2O3 grains are dispersed within the ZrO2 grains at a dispersion ratio of 2% or more, which is defined as a ratio of the number of the Al2O3 grains dispersed in the ZrO2 grains relative to the number of the entire Al2O3 grains dispersed in the ceramic material. In addition, by using the combination of CeO2 and TiO2 as the stabilizer, the grain growth of the ZrO2 grains can be enhanced moderately, so that parts of the Al2O3 grains are effectively dispersed within the ZrO2 grains, and a critical stress of a stress induced transformation from the tetragonal ZrO2 to monoclinic ZrO2 is increased.
By the way, as one potential approach for improving wear resistance and hardness of this kind of the ceramic material, it is proposed to increase the additive amount of Al2O3. However, such an increase of the Al2O3 amount generally leads to reductions in mechanical strength and toughness. In above cases, a preferred amount of Al2O3 in the composite ceramic sintered body or the ceramic material is in a range of 0.5 to 50 vol %. When the Al2O3 amount exceeds 50 vol %, Al2O3 becomes the matrix phase, so that it is difficult to maintain a strengthening mechanism based on a stress induced phase transformation of ZrO2. Consequently, considerable reductions in mechanical strength and toughness may occur.
Thus, the previous ZrO2—Al2O3 composite ceramic materials still have a problem to be solved for providing excellent wear resistance and hardness without causing reductions in mechanical strength and toughness under a larger amount of Al2O3.